A study of slow-crack propagation in zirconia-toughened alumina (ZTA) ceramics is presented. Different ZTA composites, using either unstabilized or yttria-stabilized zirconia, have been tested. The materials were prepared in the range 0-15 vol% ZrO2, using two processing methods: powder mixing and a modified colloidal route. Crack propagation tests have been conducted for crack velocities from 10(-12) to 10(-2) m/s by means of a double-torsion method. The influence of the processing conditions and compositions on the microstructures and the effect of these microstructures on the slow-crack-growth behavior have been studied. The option that these composites may offer in terms of the lifetime of ceramic joint prostheses is discussed.